1. Field of the Invention
The present invention relates to a method and a device for measuring intensity of electromagnetic field which is formed by electromagnetic waves radiated outward from various kinds of electronic device.
2. Description of the Prior Art
As a method for measuring intensity of electromagnetic field due to electromagnetic waves radiated outward from electronic device as a measure to cope with EMI (ElectroMagnetic Interference), those such as described below have been specified. As an example, nominated is a method to implement measurement with a device-under test (DUT) being a piece of electronic device as an measurement object being disposed in an open space, and with a loop antenna or a dipole antenna being disposed at a distance of 3 m to 10 m from this DUT. Thus, in the case where an antenna has been disposed at an ample distance from the DUT, the loop antenna can measure only magnetic component of the far-remote radiation electromagnetic field, and the dipole antenna can measure only electric field component thereof. And one component of the far-remote radiation electromagnetic field being measured, the other can be calculated. In addition, a method for implementing measurement not in an open space but in a radio darkroom has also been specified.
On the other hand, there is also a case where the radiation source of an electromagnetic wave is specified. For example, this takes place in the case where it is specified that from which part on a circuit substrate the electromagnetic wave is being intensively radiated. In such a case, unlike the said measurement, the intensity of electromagnetic field is measured adjacent to the DUT. In general, a small loop antenna is made to approach the DUT and the magnetic field component is measured. That is, in this method, the magnetic field component of the electromagnetic field due to the DUT is measured by using the dielectric electromotive force due to magnetic coupling. In addition, based on the result of this measurement, current-voltage distribution in the DUT is obtained and the radiation source is specified.
Incidentally, a method utilizing the said open space or radio darkroom requires a vast disposing space and a large amount of device investment. Therefore, in recent years, as an assessment method on intensity of radiated electromagnetic waves, an assessment method utilizing a coaxial transmission line called TEM Cell (Transverse ElectroMagnetic Cell) attracts public attention. In this assessment method, assessment is implemented with a DUT being disposed between interior conductor and exterior conductor of the coaxial transmission line, and based on signals to be outputted from one end of interior conductor. This method is advantageous in its capability to implement assessment with a comparatively small device.
However, the method utilizing the TEM Cell has presented a problem that it cannot give correlation with measurement in an open space. That is, the problem is that since the DUT and the interior conductor come in close vicinity to each other in terms of distance, the output current from the TEM Cell can no longer ignore the current due to magnetic coupling and the current due to electric coupling.
On the other hand, it is necessary to exclude influence by electric field component for the purpose of specifying in good accuracy the radiation source of the electromagnetic waves utilizing the said loop antenna. Therefore, shielded loop antenna in which a loop antenna has undergone shielding are often used. With this shielded loop antenna, which is hardly influenced by the electric field component, measurement only on the magnetic field component can be implemented comparatively highly accurately.
However, even with a shielded loop antenna, which will give rise to an electric field coupling between itself and the test sampling device in the section having not undergone shielding due to its configuration problems, it will be difficult to measure only magnetic field component accurately. In addition, configuration comprising shielded sections makes it difficult to implement miniaturization. That is, it was difficult to improve resolution capacity.
A purpose of the present invention is to provide a method as well as a device which can measure the electric field component and the magnetic field component respectively of intensity of electromagnetic field surrounding a DUT with small and simple device easily and accurately.
To achieve this goal, the present invention proposes a method for measuring intensity of electromagnetic field surrounding a DUT, wherein a conductor is disposed within an area where electric coupling and magnetic coupling take place between the conductor and the DUT in at least a portion of frequency band width, and the value of composite currents of a first current being outputted from the conductor due to electric coupling between the DUT and the conductor and a second current being outputted from the conductor due to magnetic coupling between the DUT and the conductor, said composite currents being outputted in a plurality of directions different from each other, is respectively measured, and based on the plurality of composite current values as well as the output direction thereof, the said first current value and the second current value are calculated, and based on the said first current value and the second current value, intensity of electric field as well as intensity of magnetic field are respectively calculated.
In the present invention, the conductor is disposed within an area where it undergoes electric coupling as well as magnetic coupling with the DUT, and therefore from the conductor, composites current of the first current due to the electric coupling and the second current due to the magnetic coupling is outputted. Here, the first current is outputted in the direction departing from the DUT being the radiation source of electromagnetic waves. On the other hand, the second current is outputted in a specific direction corresponding with the shape of conductor or positional relationship between the conductor and the DUT. That is, the values of composite currents to be outputted in a plurality of directions different from each other from the conductor to the DUT will be different values corresponding with the output directions. Accordingly, a plurality of composite current values, which are measured in different output directions, make it possible to calculate the first current as well as the second current from a plurality of measured composite current values. And, with this first and the second current values, the electric field component and the magnetic field component of the electromagnetic field can be measured accurately.
Purposes, configurations, and advantages other than the said on the present invention will become apparent in the following detailed descriptions.